The present invention relates to a method and apparatus for measuring the proportion of undissolved gas in a liquid component for the production of foam materials particularly those based on polyurethane.
To induce cell formation in the foaming reaction, a specific quantity of a gas such as air, must be contained in the reaction mixture in the form of fine bubbles to serve as nuclei in the foaming reation. Depending on the various desired foam materials, a varying quantity of gas is necessary for this nucleus formation.
For this purpose, a gas such as air is introduced into one of the reaction components, which carries the gas with it into the mixing chamber, or the gas is introduced directly into the mixing chamber. The first mentioned method has been carried out in the past because during the expansion of the component charged with gas into the mixing chamber the gas is better distributed. The term "gas charge" of the reaction component is used. This is understood to mean the quantity of gas which is contained in the reaction component in the form of undissolved finely distributed gas bubbles.
The gas, such as air, may be introduced into a reaction component, preferably into the polyol component, in the case of polyurethane foamable reaction mixtures, by means of a mixing lance or by means of a fast running stirrer in the storage container. Gas may also be introduced into a reaction compound or into a premixing chamber through porous metal plates or injection nozzles via a dosing device. Finally the components are also recirculated by means of pumps and the return flow is fed into the gas chamber of the storage container which is under supply pressure, whereby gas is absorbed.
All these methods are extremely inaccurate and uncertain and hitherto have been conducted purely according to trial and error. In previous methods therefore, control of the gas was very unstable. The only control was the visual evaluation of the finished product. If, in the case of structural hard polyurethane foam material, the color was dark brown, then it contained too little gas. If the color was light brown, the gas proportions were correctly selected. If the foam was light brown with surface bubbles, then the foam contained too much gas.
The object of the present invention is therefore to provide a method and apparatus with which gas charges are measurable, i.e. measurable in such a way as to be reproducible.